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    <script>
        // 字符串不可变性
        var str = 'andy'
        console.log(str);
        var str = 'red'
        console.log(str);
        // 因为我们的字符串不可变 所以不要大量拼接字符串
        var str = ''
        for(var i = 1; i < 1000000000; i++) {
            str += i 
        }
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